I use multi_field to index content of multiple properties into a single _all-like multi_field. Each contributing property may define different boost when defining it's instance of the multi_field. these boosts are however ignored when searching against such multi_fied while honored while searching against _all

full recreation is here https://gist.github.com/roytmana/7330956

it compares the same query against my multi_field all and ES _all